Rigid circuit board with flexibly attached module

ABSTRACT

An electrical interconnection system comprises a bifurcated, multilayer flex circuit having electrode pads on the inner surfaces of the bifurcation. Electronic components are mounted on one or both sides of the flex circuit by conventional means. When the bifurcation is spread apart, the electrode pads are alignable with respective contacts on a printed circuit board. After bonding the pads to the contacts by soldering, conductive adhesive, or other means, a secure electrical connection is maintained while still allowing the flex circuit to bend somewhat from side to side, creating additional design options not available with rigidly mounted components and modules.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. patent application Ser. No.13/573,976, filed on Oct. 17, 2012 by the present inventors, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to means for connectingmicroelectronic devices and systems. More particularly, the inventionrelates to improved flex-circuit based interconnect solutions forelectronic circuits.

Description of Related Art

The evolution of smaller, lighter electronic devices withever-increasing functionalities has increased the need for packaging,mounting, and interconnection architectures that will reduce size andweight while at the same time preserving interconnection characteristicsthat can handle the flow of large amounts of data between variouscircuits or modules in a device. Flex circuits are often used to providea signal routing means that can be easily located in confined placeswithin an equipment enclosure. They are also used to maintain electricalconnections between two components that must move relative to oneanother; examples are the connections between the motherboard and thedisplay on a laptop computer, or in many cell phones.

Various approaches have been used to enable a long, flexible circuit tobe reliably connected to a component such as a motherboard. In one case,a socket is permanently installed on the motherboard (typically bysoldering). A mating plug is affixed to the end of the flex bymechanically clamping or crimping; this plug contains internal metalpins that pierce the flex to complete an electrical connection betweenthe lines on the flex and the contacts on the plug that will mate withcorresponding contacts on the socket. As the number of lines increases,and the pitch becomes correspondingly smaller, both the cost andreliability of this approach can suffer.

Another approach, used particularly when the flex connection might needto withstand especially demanding mechanical forces, is to affix rigidcircuit boards on both sides of the flex near the terminations. Theseboards typically have plated through holes and can be placed flatagainst the motherboard to secure a strong soldered connection.Connectors may also be further strengthened by potting in epoxy.

Objects and Advantages

Objects of the present invention include at least the following:providing a flex circuit board and interconnect system having reducedsize and complexity; providing a low-cost, highly reliable flex circuitboard or module and associated interconnect system; providing a morereliable and manufacturable flex circuit board or module suitable fordirectly mounting on a motherboard without additional packaging;providing a motherboard with flex circuit boards mounted thereon via acompliant interconnect; and, providing a method for manufacturing flexcircuits that is cost effective and suitable for mounting directly on amotherboard without a separate socket.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a flexible circuit boardcomprises: a multilayer flex circuit having bifurcated extensions alongone edge thereof and a plurality of electronic components mounted on atleast one surface thereof; and a plurality of electrode pads positionedon the inner and/or outer surfaces of the two legs of the bifurcatedextensions such that when the legs are spread apart by about 180° theelectrode pads are alignable with respective contacts on a motherboard,and/or on a clamping connector and connectable thereto, so that asecure, mechanically flexible connection may be created between theflexible circuit board and the motherboard.

In accordance with another aspect of the invention, an electricalcircuit comprises: a rigid printed circuit board or motherboard having aplurality of electrical contacts on at least one surface thereof: amultilayer flexible circuit board having a plurality of electricalcomponents on at least one surface thereof, and further having abifurcated area along one edge thereof; electrode pads on the innersurfaces of the bifurcated area of said flexible circuit board that arealigned respectively with electrical contacts on the rigid circuit boardwhen the legs of the bifurcation are spread apart by about 180°; and,electrical connections between the electrode pads and the respectiveelectrical contacts sufficient to maintain electrical continuity andmechanical flexibility between the rigid printed circuit board and theflexible circuit board.

In accordance with another aspect of the invention, a method for makingan electrical circuit comprises the steps of:

forming a rigid printed circuit board having a plurality of electricalcontacts on at least one surface thereof;

forming a multilayer flexible circuit board having a plurality ofelectrical components on at least one surface thereof, and furtherhaving a bifurcated area along one edge thereof;

forming electrode pads on the inner surfaces of the bifurcated area ofthe flexible circuit board that are alignable respectively with theelectrical contacts on the rigid circuit board when the bifurcated areais spread apart by about 180°;

spreading the bifurcated area apart and aligning the electrode padsrespectively with the electrical contacts; and

forming an electrical connection between the electrode pads and theelectrical contacts.

In accordance with another aspect of the invention, an electronicsubsystem comprises: a rigid circuit board daughter card or substratehaving a plurality of electrical components on at least one surfacethereof and electrical contacts along one edge thereof, one or moreflexible circuit leads having a plurality of electrical contacts inelectrical communication with the electrical contacts of the rigidprinted circuit board thereof, and further extending at an angle alongat least one edge thereof; electrode pads on at least one surface ofsaid extension alignable with respective contacts on a motherboard,and/or clamping connector and connectable thereto, so that an electricaland secure, mechanically flexible connection may be created between saidrigid circuit board daughter card and said motherboard.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically a bifurcated flexible circuit havingcontact pads on the inner and outer surfaces of bifurcated extensionsaccording to one aspect of the invention.

FIG. 2 illustrates schematically a bifurcated flex circuitdirect-mounted on a printed circuit board or motherboard.

FIG. 3A illustrates the flexible or compliant properties of bifurcatedflexible circuits direct-mounted on a motherboard according to anotheraspect of the invention.

FIG. 3B illustrates the flexible or compliant properties of bifurcatedflexible circuits direct-mounted on a motherboard within an enclosureaccording to another aspect of the invention.

FIG. 4A illustrates a supporting device to prevent excessive flexurebetween bifurcated flexible circuits that are vertically mounted on amotherboard according to another aspect of the invention.

FIG. 4B illustrates a supporting device to prevent excessive flexurebetween bifurcated flexible circuits that are mounted at an obliqueangle to a motherboard according to another aspect of the invention.

FIG. 5 illustrates schematically a rigid printed circuit board adaptedwith flexible circuit leads having contact pads on the inner surfacesfor direct-mounting on a printed circuit board or motherboard accordingto one aspect of the invention.

FIG. 6 illustrates schematically a bifurcated flex circuitdirect-mounted on a printed circuit board or motherboard by means ofconductive spheres or bumps, according to another aspect of theinvention.

FIG. 7 illustrates schematically a bifurcated flex circuitdirect-mounted on a printed circuit board or motherboard by means ofcompression clamps, according to another aspect of the invention.

FIG. 8A illustrates schematically a bifurcated flex circuitdirect-mounted on protruding pins, soldered to a printed circuit boardor motherboard, by means of compression clamps, according to anotheraspect of the invention.

FIG. 8B illustrates schematically a bifurcated flex circuitdirect-mounted on protruding pins, soldered to a printed circuit boardor motherboard, by means of compression clamps that include flex circuitconnectors, according to another aspect of the invention.

FIG. 9 illustrates schematically a bifurcated flex circuitdirect-mounted to a printed circuit board or motherboard, by means ofcompression clamps that include integral compression posts, according toanother aspect of the invention.

FIG. 10A illustrates different patterns for piercing the electrode padson the bifurcated extensions, according to one aspect of the invention.

FIG. 10B illustrates in cross-section the deformation of a piercedelectrode pad when compressed by a post, according to one aspect of theinvention.

FIG. 10C illustrates in cross-section a pierced electrode pad adjacent alayer of compliant material that enables a controlled deformation of thepad when a force is applied against a contact pin.

FIG. 11A illustrates schematically a bifurcated flexible circuit havingcontact pads on the inner surfaces of bifurcated extensions which areinserted through a slot within a clamping collar, according to oneaspect of the invention.

FIG. 11B illustrates schematically a bifurcated flexible circuit havingcontact pads on the inner surfaces of bifurcated extensions which areinserted through a slot within a clamping collar and partially or fullyreflexed against the bottom surface thereof, according to one aspect ofthe invention.

FIG. 11C illustrates schematically a bifurcated flexible circuit havingcontact pads on the inner surfaces of partially reflexed bifurcatedextensions which are inserted through a slot within a clamping collarfor attachment to a test socket, according to one aspect of theinvention.

FIG. 11D illustrates schematically a bifurcated flexible circuit havingcontact pads on the inner surfaces of partially reflexed bifurcatedextensions which are inserted through a slot within a clamping collarfor attachment to a Zebra Strip Connector, according to one aspect ofthe invention.

FIG. 11E illustrates a bifurcated flexible circuit formed using twoseparate flexible films laminated to the outer surfaces of rigid PCBsubstrate, similar to FIG. 5, but which extend under the electroniccomponents mounted to the sides. The bottom contacts include pads onboth the inner and outer surfaces of the flexible films, which caninterface with a socket connector.

FIG. 12A illustrates schematically the side-view of a bifurcatedflexible circuit inserted through a slot within a clamping collar forattachment to a compression latch assembly, according to one aspect ofthe invention.

FIG. 12B illustrates schematically the bottom-view of the clampingcollar of FIG. 12A with a center slot and alignment posts for attachmentto a compression latch assembly, according to one aspect of theinvention.

FIG. 12C illustrates schematically the bottom-view of the flexiblebifurcated extensions of FIG. 12A with circuit leads and conductivebumps for attachment to a motherboard by means of a compression latchassembly, according to one aspect of the invention.

FIG. 12D illustrates schematically a side-view of an interposer boardfor adding gold-plated contacts onto the surface of a motherboardcompatible with a compression latch assembly, according to one aspect ofthe invention

FIG. 12E illustrates schematically the side-view of a bifurcatedflexible circuit inserted through a slot of a bowed clamping collar forattachment to a compression latch with integral, press-fitted, stampedmetal contacts, according to one aspect of the invention.

FIG. 12F illustrates schematically the front and side-views of stampedmetal straight contacts, according to one aspect of the invention.

FIG. 12G illustrates schematically a cross-section view of staggered,stamped metal straight contacts press-fitted into a compression latchassembly, according to one aspect of the invention.

FIG. 12H illustrates schematically a top-view of staggered, stampedmetal straight contacts press-fitted into a compression latch assembly,according to one aspect of the invention.

FIG. 12J illustrates schematically the front and side-views of stampedmetal “J-bend” contacts, according to one aspect of the invention.

FIG. 12K illustrates schematically a cross-section view of staggered,stamped metal “J-bend” contacts press-fitted into a compression latchassembly, according to one aspect of the invention.

FIG. 12L illustrates schematically a top-view of staggered, stampedmetal “J-bend” contacts press-fitted into a compression latch assembly,according to one aspect of the invention.

FIG. 12M illustrates schematically the front and side-views of stampedmetal spring contacts, according to one aspect of the invention.

FIG. 12N illustrates schematically a cross-section view of staggeredstamped metal spring contacts press-fitted into a compression latchassembly, according to one aspect of the invention.

FIG. 12P illustrates schematically a top-view of staggered, stampedmetal spring contacts press-fitted into a compression latch assembly,according to one aspect of the invention.

FIG. 13 illustrates schematically a cross-section view of a bifurcatedflexible circuit, protected within two metal heat spreaders havingangled flanges, with bifurcated extensions bonded to the bottom of theangled flanges, according to one aspect of the invention.

FIG. 14 illustrates schematically a cross-section view of a bifurcatedflexible circuit, protected within two metal heat spreaders havingdiverging flanges, with bifurcated extensions bonded to the bottom ofthe diverging flanges, according to one aspect of the invention.

FIG. 15A illustrates schematically a cross-section view of a bifurcatedflexible circuit, protected within two metal heat spreaders havingangled flanges, clamped in compression against a motherboard with metalwedges, according to one aspect of the invention.

FIG. 15B illustrates the embodiment of FIG. 15A with a bifurcatedflexible circuit having a folded extension with additional components,protected within metal heat spreaders without flanges, according to oneaspect of the invention.

FIG. 15C illustrates schematically a cross-section view of a bifurcatedflexible circuit, protected within two metal heat spreaders withoutflanges, clamped in compression horizontally against a motherboard witha clamping device, according to one aspect of the invention.

FIG. 15D illustrates the embodiment of FIG. 15C, which includes a foldedextension with additional components, protected within metal heatspreaders without flanges, clamped in compression horizontally to thetop surface of a motherboard with a single clamping device, according toone aspect of the invention. FIG. 15E illustrates the embodiment of FIG.15C clamped in compression horizontally on both sides of a motherboardwith two clamping devices, according to another aspect of the invention.

FIG. 16A illustrates schematically a top-view of a direct connect socketfor bifurcated flexible circuits protected within metal heat spreadershaving angled flanges, according to one aspect of the invention.

FIG. 16B illustrates schematically a side-view of a direct connectsocket for bifurcated flexible circuits protected within metal heatspreaders having angled flanges, according to one aspect of theinvention.

FIG. 16C illustrates schematically a cross-section view of a pivotingcompression clamp for metal heat spreaders having angled flanges,according to one aspect of the invention.

FIG. 17A illustrates schematically a top-view of a direct connect socketfor bifurcated flexible circuits protected within metal heat spreadershaving diverging flanges, according to one aspect of the invention.

FIG. 17B illustrates schematically a side-view of a direct connectsocket for bifurcated flexible circuits protected within metal heatspreaders having diverging flanges, according to one aspect of theinvention.

FIG. 17C illustrates schematically a cross-section view of a pivotingcompression clamp for metal heat spreaders having diverging flanges,according to one aspect of the invention.

FIG. 18A illustrates schematically a cross-section view of an interposerboard having bladed contacts and a concave dimpled clamping collar formechanical forming and electrical mating with the electrode pads of abifurcated flexible circuit, according to one aspect of the invention.

FIG. 18B illustrates schematically a close-up, cross-section view ofFIG. 18 A.

FIG. 18C illustrates schematically a cross-section view of a convexdimpled clamping collar for mechanical forming and electrical matingwith the electrode pads of a bifurcated flexible circuit, according toone aspect of the invention.

FIG. 18D illustrates schematically a close-up, cross-section view ofFIG. 18 C.

FIG. 19 illustrates schematically the bifurcated flex circuit of FIG. 2direct-mounted on both the top and bottom surface of a printed circuitboard or motherboard using shared contacts of the motherboard by meansof a contact translation board.

FIG. 20 illustrates schematically the bifurcated flex circuit of FIG. 2direct-mounted to the edge of a printed circuit board or motherboardusing a sliding compression connector.

DETAILED DESCRIPTION OF THE INVENTION

The concept of a bifurcated flex circuit board is taught Applicants'U.S. patent application Ser. No. 12/317,757, as well as in Applicants'issued U.S. Pat. Nos. 7,796,399, and 7,724,530. The entire contents ofall of the foregoing are incorporated herein by reference. Theaforementioned disclosures are directed to various ways of making rigidmodules, particularly DRAM modules, for rigidly mounting onto amotherboard via a rigidly-mounted socket or by soldering or adhesivebonding directly onto contacts on the motherboard The present inventionis based on Applicants' recognition that a multilayer, bifurcated flexcircuit board can be mounted directly onto a motherboard in such a waythat the mounting is flexible (i.e., it can allow the flex circuit tobend from side to side to some degree) and yet maintains electricalconnectivity to the motherboard. As will be illustrated in the followingexamples, this structure provides numerous surprising advantages overconventional rigidly-mounted electronic modules. Some of theseadvantages include the following: 1. Size, weight, and cost of theentire system can be reduced by eliminating much of the module-levelpackaging. 2. Heat-generating components may be more effectively cooledby eliminating layers of packaging' including surrounding socketstructures which may impede air flow along the modules. 3. Assemblymethods can take advantage of the compliant mounting of subsystems,allowing them to be folded sideways to reduce the height of thepopulated motherboard.

FIGS. 1-3 illustrate electronic subsystems 1, 1′ and 1″ in which acentrally located, multilayer, bifurcated flexible circuit board orsubstrate 10 is populated on one or both sides with various electroniccomponents 11, which are connected by vias to circuit lines or traces onthe inner and external surfaces of the individual dielectric plies. Inthe examples shown, two individual plies, with circuit traces on bothsurfaces, are bonded or laminated together with an adhesive or film 9 atthe middle of the sandwich and interconnected with vias. Along one edge,the two flexible plies are bifurcated into two extensions or legs 13 byeither selective application or removal of the middle bonding adhesiveor by peeling the edges apart if the laminate plies are weakly bonded.In this example, electrode pads 12 are arranged along the inner surfacesof the bifurcated extension and electrode pads 12′ are arranged alongthe outer surfaces of the two bifurcated legs. Spreading the two legs ofthe bifurcated area apart, typically by about 180°, exposes pads 12 andenables them to be aligned with respective contacts 21 on a rigidprinted circuit board or motherboard 20 as shown in FIG. 2. The pads arethen bonded to the contacts using solder, anisotropic conductiveadhesive, or isotropic conductive adhesive, or by clamping them incompression against the contacts, thereby functionally connecting thesubsystem 1 to the motherboard. At the same time, there is a sufficientlength of the legs 13 of the bifurcated flexible circuit board to allowthe flex board to move from side to side by a useful amount. (As usedherein, a useful amount of flexure might be as little as a few degreesor as much as +/−45° or even 90°, as shown generally in FIG. 3.)

It will be appreciated that as used herein, the term “motherboard” isnot limited specifically to a circuit board that includes a computer'sCPU, but instead simply refers to any substantially rigid printedcircuit board on which various components and subsystems may be mountedto form a higher-level electronic system. It will be further appreciatedthat the invention may be applied to desktop computers, mobilecomputers, tablet computers, smart phones, servers, and virtually anyelectronic system in which one needs to attach a multi-componentsubsystem to a larger system.

EXAMPLE

FIG. 1 illustrates schematically a bifurcated flexible circuit board 10.The board may be constructed by forming two individual flexibledielectric sheets using polyimide or other suitable substrate materialhaving selected metallization patterns as are well known in the art.Each sheet has electronic components 11 mounted on one side (which forclarity will be referred to as the outer surface) and a metallizationpattern, including electrode pads 12 on the other side. Each sheet willtypically have conductive vias that interconnect the two sides of thesheet, thereby allowing signals to move between the components 11 andpads 12.

In one embodiment of FIG. 1, the bifurcated flexible circuit board 10consists of an Organic Light Emitting Diode display (OLED) adapted fordirect connection to a PCB or motherboard 20 as explained below.

The two sheets are bonded together with an adhesive film 9 over most oftheir surface area, leaving a bifurcated area forming two extensions 13along one edge. The flexible board will also preferably extend for somedistance between the mounted components 11 and the extensions 13 tocreate a compliant region 14.

EXAMPLE

FIG. 2. illustrates a subsystem 1 mounted onto motherboard 20. Contacts21 on motherboard 20 are spaced so that they will align with theirrespective electrode pads 12 on the flex board of subsystem 1. Alignmentholes may be located near the center and/or ends of the length of thebifurcated extensions or legs 13, as shown at 57 in FIG. 12C, to aid inthe alignment of the electrode pads 12 with the contacts 21 on themotherboard. When pads 12 are bonded or compressed against contacts 21,the subsystem 1 is securely attached to motherboard 20, and yet has adegree of flexibility as shown schematically in FIG. 3A. It will beappreciated that if pads 12′ are disposed on the outer surfaces of thelegs 13 as shown in FIG. 1, another mounting option is available (notshown): In this option, the motherboard can have a slot through whichcompliant region 14 is passed. Legs 13 are then opened to bring pads 12′into alignment with contacts on the underside of motherboard 20.

The contact pads on the motherboard of FIG. 2 may be either of theSurface Mount Technology (SMT) type or through-hole type, asillustrated.

EXAMPLE

The inherent flexibility of the inventive interconnection systemprovides the system designer with many opportunities to optimizesystem-level layout and assembly as shown in FIG. 3B. Here, motherboard20, having two subsystems 1′ and 1″ and another component 22 mountedthereon, must be packaged into housing 30. After bonding to motherboard20, subsystem 1′ is flexed clockwise by about 45° and subsystem 1″ isflexed counterclockwise by about 90° to accommodate the geometricalconstraints imposed by the system requirements. For applicationsrequiring subsystems 1″ to be flexed up to 90° the adhesive or bondingfilm 9 used to laminated the flexible layers of plies together may beadjusted to lengthen the bifurcated area and legs 13, as shown in FIG.3B.

EXAMPLE

The electronic components 11 mounted on the flex board may be of anytype, such as, for example, logic devices and microprocessors, memorychips including DRAM or flash, buffer and timing circuits, analog,digital, and mixed-signal circuits, RF devices, optoelectronic devicesincluding LEDs, and passive components including resistors, capacitors,inductors, and antennas. Furthermore, components 11 may be of anysuitable size or form, such as, for example, bare die, packaged die,surface-mount, BGA, multichip module, etc., and the components may beattached to the flex board using any conventional technique such assolder, epoxy and wire bonds, or various conductive adhesives as arewell known in the art.

EXAMPLE

The invention may be used for mounting one or more rows of DRAM chipsonto a motherboard, where a key advantage of the invention is that theindividual chips are more easily cooled by flowing air because much ofthe traditional package requirements of a conventional DRAM module isreduced or eliminated (e.g. module width/height or socket obstruction).It will be appreciated, however, that when a large flow of coolant isexpected, it will in some cases be desirable to constrain the flexure ofthe subsystem 1 relative to the motherboard 20 so that unconstrainedharmonic oscillations won't lead to fatigue and premature mechanicalfailure of the interconnects. FIG. 4A illustrates an enclosure 30′having slots 40 along the top inner surface. Slots or other mechanicalconstraint structures may alternatively be attached to motherboard 20instead of to enclosure 30′.

EXAMPLE

As noted earlier, in some cases, it is desirable to orient the subsystem1 at some angle relative to motherboard 20 in order to reduce the systemprofile as shown generally in FIG. 3B. In these situations, if flowingcoolant is also used, a reduced-height enclosure 30″ may employ angledslots 40′ to hold the flex boards at a selected angle relative tomotherboard 20. A solution of this type might be appropriate forapplications such as blade servers, for example.

Those skilled in the art will appreciate that the invention is notlimited to particular applications such as DRAM, but in fact is ageneral solution to many electronic systems and interconnectionproblems.

EXAMPLE

The inventive circuit is preferably manufactured as follows. First, twoindividual flexible circuit plies or laminates having conductive traces(typically on both surfaces) and vias connecting one surface to theother and one ply to another as needed, are formed by conventional meansand bonded together over most of their surface area to form a multilayerflex panel or circuit board, leaving an unbonded strip (bifurcation)along one edge. The electrode pads intended to connect this circuit to amotherboard are located on the inner surfaces of the bifurcation. Next,the flex circuit is populated by microelectronic devices, which may beany combination of analog, digital, or mixed-mode semiconductor devicesor passive components. This step will typically involve conventional“pick and place” assembly using solder or conductive adhesives as areknown in the art. Then, the two legs of the bifurcated extensions orarea are spread apart and the electrode pads are aligned with rows ofcontacts on a motherboard. The pads on the flex are then joined to thecontacts using solder or conductive adhesive, by which the flex issecurely held onto the motherboard but still able to bend from side toside by an amount that will be controlled to some degree by the rigidityof the flex and its overall geometry.

Applicants contemplate that for some applications, a soldering bondingtechnique will be used to affix the flex circuit to the rigid circuitboard. Alternatively, adhesive bonding using isotropic or anisotropicconductive adhesives may also be used as is well known in the art ofelectronic assembly. Each of the above mentioned techniques result in apermanent or semi-permanent mating of the flex circuit to the rigidcircuit board or motherboard. In other cases, however, a detachablemating of the aligned pads and contacts will be the preferred method andvarious clamping devices, collars and compression latch assemblies aredisclosed for this purpose. A variety of novel clamping devices are alsodisclosed herein to enable the flexible extensions to be temporarily, orsemi-permanently compressed against various pads, plated through-holes,pins, compressible springs or conductors, and interposers.

The invention may also be modified to use with rigid circuit boards.Referring now to FIG. 5, an electronic subsystem 2, with a rigid circuitboard or substrate 15 in place of a flexible circuit, is illustrated incross-section with four rows of electronic components 11 in astandard-height DIMM memory module. In order to adapt the rigid circuitboard for direct connection to the motherboard 20, flexible circuitleads 16 are electrically and mechanically attached to the DIMM padsalong the bottom sides and spread apart to about 180° to enableelectrode pads 12 to connect to contacts 21 on the PCB or motherboard20. In this manner, a rigid printed circuit board module can be adaptedfor mounting at various angles with the respect to the motherboard aspreviously described in FIG. 3A.

In an alternative embodiment of FIG. 5, the rigid circuit board orsubstrate 15 consists of a Liquid Crystal Display (LCD) adapted fordirect mounting to a PCB or motherboard 20 using bifurcated flexiblecircuit leads. In another alternative embodiment of FIG. 5, the rigidcircuit board or substrate 15 consists of a Rigid-Flex Circuit Boardadapted for direct mounting to a PCB or motherboard 20 using bifurcatedflexible circuit leads.

FIG. 6 illustrates a design for enabling electronic subsystem 1, with abirfurcated flexible circuit board or substrate 10, to be directly matedto a motherboard 20. Electrode pads 12, arrayed along the bottom, insidesurfaces of the birfurcated area are exposed when legs 13 are bent apartin such a manner to form a 180° angle to mate with motherboard 20. Theangle illustrated here between each leg 13 and flexible circuit board 10is approximately 90°; however, other angles may likewise be implemented.In this example, an array of conductive spheres or bumps 17 are disposedon electrode pads 12 to enable the pads to self-align and electricallymate with appropriately sized annular rings 19 of plated-through holes(PTHs) 18 arrayed on the motherboard 20. Conductive spheres or bumps 17may be fashioned from a large variety of materials, including; plated orpartially reflowed solder balls, plated metal columnar bumps, goldthermo-compression bonded balls or stud bumps, stenciled or dispensedconductive epoxy or conductive elastomeric material, or anisotropicconductive adhesive and other means known for establishing electricalconnection between flex circuit electrode pads 12 and PTH annular rings19 or contacts 21 (not shown) of motherboard 20. Conductive spheres madeusing solder alloys enable the electrode pads to be directly soldered toeither the pads or plated-through holes of the motherboard. For example,if the flex circuit pads are simply coated with solder by plating ordipping in a molten bath, or if solder paste is stenciled or dispensedonto the motherboard contacts, the pads and contacts can then besubsequently soldered together by aligning them and using a heater-barto simultaneously compress and melt the solder. Alternatively, if theconductive spheres are fashioned from either a rigid or compressibleconductive material, they may be removably mated to the motherboardcontacts using various means for applying a clamping force between thetwo surfaces.

In many instances it will be preferable for electronics subsystem(s) 1to be removably mounted to the motherboard 20. FIG. 7 illustrates anexample of a clamping device 22 for applying a compressive force againstthe backside of the bifurcated extensions 13 to establish electricalcontact between the PTH annular rings 19 and conductive spheres 17 onelectrode pads 12 fashioned from plated metal bumps. Conductive spheres17 are designed with a diameter slightly larger than the inside diameterof the PTH vias 18 such that when a compressive force is applied theplated metal conductive spheres 17 enter into intimate, gas tight,electrical contact with the inside perimeter of the PTH annular rings19. This electrical contact is maintained as long as the compressiveforce is maintained. Conversely, when the compressive force maintainingthe electrical connection is removed, electronic devices or electronicsubsystems 1 can be removed from the motherboard without need of ade-soldering process. Compressive force in FIG. 7 is provided using ascrew 23 and a lock nut 24 to apply a clamping force against thebackside of the bifurcated extensions 13. The plated metal conductivespheres 17 are positioned on electrode pads 12 to align and mate withthe inside perimeter of the PTH annular rings 19 typically used forreceiving and soldering the DIMM socket's pins. These sockets typicallyrequire four adjacent rows of staggered PTH vias 18 on the motherboardthat receive the socket pins for soldering. The plated metal conductivespheres align with each via of the motherboard in a similar staggeredconfiguration. For purposes of this compression contact, it ispreferable that both the conductive spheres and PTH vias are plated withgold or other noble metal to ensure reliable electrical conductivity.Normal force is applied and maintained to these plated bumps using aclamping device 22. One simple clamping device would consist of a metalbracket with a compliant material 25 on the bottom surfaces that iscompressed against the surface of the motherboard 20 and flexiblecircuit extensions 13. The compliant material 25 may be composed ofrubber, silicone, or other material with elastomeric properties, whichcan be bonded to the surface of the metal clamping device. As notedearlier, other materials can be substituted for the plated metalconductive spheres 17, such as a “Zebra Strip” (i.e., conductiveelastomeric material), for achieving electrical connection whencompressed between electrode pads 12 and PTH annular rings 19.

FIG. 8A is similar to FIG. 7, but illustrates a different contacttechnique for the electronic subassembly 1. In this embodiment,conductive spheres 17 are replaced with a “bed-of-nails” connector 26that includes an array of pins extending from the bottom of motherboard20, through the PTH vias 18, and projecting slightly above the PTHannular rings 19. Connector 26 includes a molded plastic “rail” to holdthe pins in proper alignment for simultaneous insertion into themotherboard vias and to set the correct stand-off height of the pinsabove the PTH annular rings. For this application the protruding pins 27would preferably be made of stamped metal with pointed or blunt tipsthat are selectively gold plated and soldered from the bottom to formsolder fillets 28 around the shaft of each pin and bottom annular ringsif the PTH vias. The compliant material 25, opposite the electrode padsof the bifurcated extensions, helps the pads to conform to the shape ofthe protruding pins and compensates for any non-uniformity in the heightof the pins. Once the pins 27 are soldered to the motherboard, theplastic rail may optionally be removed. If the pins are wave solderedfrom the bottom side of the mother board, the solder would typicallyform solder fillets 28, as shown. The advantage of this connectorconcept is that the electrical signal path from the motherboard into thesubassembly is kept to a minimum distance and should therefore exhibitless parasitic capacitance and/or inductance with higher signal speeds.Although only two rows of connector pins are illustrated incross-section for FIG. 8, it should be understood that there wouldpreferably be four rows of staggered protruding pins 27 that match themounting footprint of standard 240-pin DIMM memory module sockets asviewed from above the motherboard.

In recent years there has been an increasing recognition for the need toincrease the number of contact pins or pads on high-density, high-speed,memory modules to provide more power and ground connections to themodules. The additional power/ground connections aid in balancing thepower and ground requirements for higher speed memory components and inproviding better signal integrity of input/output signals. Normally thiswould be achieved by reducing the pad-to-pad pitch on the modules andcorrespondingly increasing the number of socket pins which contact thesemodule pads. But, the number of contact pins on traditional DIMM socketsseems to have reached a practical limit at its current level of 240 pinsdue to the excessive insertion and extraction forces required. Many OEMmanufacturers are experiencing problems with module and socket breakageduring insertion of the modules and the problem is exacerbated ifautomated equipment is used for this manufacturing step. The embodimentshown in FIG. 8B is an attempt to help solve this problem.

The electronic subsystem 1 and “bed-of-nails” connector 26, as shown inFIG. 8A, are similar to FIG. 8B, but the bifurcations now include bothbottom electrode pads 12 and top electrode pads 12′, similar to FIG. 1,and clamping device 22′ is modified to include an integrated flexcircuit connector 50 with integrated conductive spheres or bumps 17. Theflex connectors 50 with conductive bumps 17 are clamped and held incompression against top electrode pads 12′ and contacts 21 on themotherboard 20 while simultaneously pressing the bottom electrode pads12 against the protruding pins 27. Flex connectors 50 also includecircuit traces that are routed between the conductive bumps 17 whichsimultaneously contact the top electrode pads 12′ and PCB contacts 21.This configuration effectively doubles the number of input/outputcontacts for electronic subsystem 1 without requiring a significantincrease in the amount of compressive normal forces. It should be noted,however, that a similar increase in the number of input/output contactscan be achieved for the embodiments represented in FIGS. 7 and 8A bysimply reducing the pad-to-pad pitch of electrode pads 12 and PTH vias19 without requiring a significant increase in the amount of compressivenormal forces.

Turning now to FIG. 9, another configuration 22″ of the clamping deviceis illustrated. This clamping device integrates compression posts 29opposite each electrode pad on the bifurcations to selectively deformthe electrode pads 12 in a manner that causes them to protrude into theapertures of the PTH vias and against the interior edges of the PTHannular rings. The resulting formed electrode pads 31 and compressiveposts 29 are engineered to provide reliable electrical connections byproviding constant contact force between pads 12 and the PCB ormotherboard vias during temperature cycling of the components. Since theposts will require constant force against the pads, it is preferablethat they be fashioned from metal or a rigid plastic. It will beappreciated that the deformation process is aided by the thincross-sectional thickness and inherently deformable characteristics ofthe bifurcations. However, additional modifications to the electrodepads 12 on the bifurcations, as represented in FIGS. 10A-C, can improveand assist in the deformation of the formed electrode pads 31 to betterengage the PTH on the motherboard 20.

FIG. 10A illustrates a single electrode pad 12, as viewed from above thepad, with four examples of various slitting patterns or shapes toproduce a pierced electrode pad 32. From left-to-right the patterns haveeither four or three slits with and without a center aperture. The slitswould extend through the entire cross-sectional thickness of theelectrode pad 12, and allow a compression post 29 to more easily deformeach slotted portion of the electrode pad 33 to conform with theinterior aperture of each PTH via 18 as represented in FIG. 10B.Referring then to FIG. 10B, an enlarged cross-sectional view of the PTHvia 18, electrode pad 12, pierced electrode pad 32, and compression post29 is illustrated. The figure on the left illustrates a view of themating surfaces before the compression post engages with the piercedelectrode pad, while the illustration to the right shows the matedsurfaces after the post presses the pierced electrode pad down into thePTH via 18 and spreads and compresses the slotted portions of theelectrode pad 33 against the interior edges of the PTH aperture ring.The inventive slits or other piercing features will help the flexconform to a dimpled surface in either a convex or concave direction.

FIG. 10C shows another cross-section example of pierced electrode pad 32with a compliant material 25 placed on the opposite surface of theflexible circuit. When a force is applied from above, as illustrated bythe bold arrow, the compliant material will allow the pads 12 to deformin a controlled manner against a metal contact pin 76, similar to thatas shown at 33 in FIG. 10B.

Applicants contemplate the principles described above for FIGS. 10A-Ccan be applied in general to other interconnect applications involvingflexible circuits, including the examples illustrated in FIGS. 12E-H,FIGS. 17A-B and FIGS. 18A-D. The principles described above allowflexible circuit connectors or sockets to be fashioned without thenecessity for using piercing pins, thereby reducing cost, enabling lowerprofile connections and adding electrical redundancy.

In the preceding “removable” electronic subsystems of FIGS. 7, 8A-B, and9, the clamping devices rely on threaded screws 23 and lock nuts 24positioned to the sides of the devices to apply the required compressivenormal forces to achieve electrical contact between the bifurcatedelectrode pads and PTH annular rings or vias of the motherboard. Theextended portions of the clamping devices that hold these screws andlock nuts reduce the available mounting area on the motherboard forother adjacent subsystems such as parallel banks of memory modules.Ideally, manufacturers prefer to reduce the amount of space or pitchbetween components in order to increase the functionality of themotherboard for a given fixed board size or enclosure. Since memoryrequires a significant amount of the available space on mostmotherboards, it is highly desirable to place the individual memorymodules as close as practical without impeding the air circulation orability to insert and remove the modules from the DIMM socketspre-soldered on the motherboard. Accordingly, a novel clamping collar 38is integrated with the bifurcations 13 for the electronic subsystemsillustrated in FIGS. 11A-D, 12A, and 12E to simplify themounting/unmounting and reduce the width necessary for clamping theremovable modules to the motherboard.

Turning now to FIG. 11A, a cross-section view is illustrated of anelectrical subsystem 1, similar to FIG. 1, with a multilayer flexiblecircuit 10, four rows of components 11 and bifurcations 13. Surroundingthe compliant region 14 (refer to FIG. 1) of the bifurcated leads is aclamping collar 38 with an open slot 47 along the centerline of thecollar that allows the extensions to be inserted through the collar. Thecollar is preferably metal or a rigid molded plastic suitable fortransferring the compression forces along its lateral length. On thebottom of the collar is a layer of compliant adhesive material 25 forbonding the bifurcations 13 to the bottom surface of the collar whenthey are spread apart (FIG. 11B). The resulting integrated clampingcollar enables the electronic subsystem or module to be mated directlywith the pads or PTH vias on the motherboard, as shown in FIG. 12A-B, orto a variety of socket pins or springs, as shown in FIG. 12E-P.

Another novel clamping collar 38′ is illustrated in FIG. 11C. The collarincludes an open slot 47′ that is tapered towards the top and sized tomate with a narrow contact post 54, the bottom leads of which aresurface mount soldered to the motherboard 20. The clamping collar 38′ isdesigned to apply a lateral, inward clamping pressure against bothflexible legs of the bifurcation when the collar 38′ is pressed downwardand over the contact post. When fully seated, the clamping collar locksthe leads to the post and pinches the electrode pads 12 against theprotruding spring pins 53 of the contact post 54. One particular problemis resolved with this type of connector system. After components 11 areassembled to the flexible bifurcated circuit 10, it is highly desirableto perform an electrical functional test of the components and assemblyconnections prior to proceeding to the next assembly steps. However,electrode pads 12 are typically disposed on the inner surfaces of theflexible plies making test probe access difficult. The clamping collarand contact post, as described above, therefore serve, among otherthings, as a novel solution to simplify electrical testing of electronicsubsystems 1 or unpopulated, bare, bifurcated flexible circuits 10 priorto component attachment. In addition, clamping collar 38′ may also beimplemented in a connector system for production mounting of modules tothe motherboard.

In the proceeding examples the flexible circuit leads were formed at an180° angle. However, the flexible leads shown in FIGS. 11C-D and FIG. 20are opened slightly while keeping the two halves approximately parallelto engage contacts on both sides of a connector or edge of a PCB ormotherboard.

FIG. 11D is similar to FIG. 11C, but illustrates that a “Zebra-strip”elastomeric connector 55, similar to those manufactured by FujipolyAmerica Corp., can replace or be integrated with the contact post 54(not shown) to achieve the same results described above.

FIG. 11E is similar to FIG. 5, but includes two separate flexiblecircuits laminated to the external surfaces of a rigid printed circuitboard (PCB) or substrate 15 and which extend under the attachedelectronic components 11. The PCB or substrate and flexible circuits maybe electrically connected across the interface of the laminatedsurfaces. Conversely, the PCB or substrate may serve only as a spacer toseparate components 11 mounted to inner surfaces of the separateflexible circuits 10 (not shown).

In this example, the two separate flexible circuits form equivalentbifurcated flexible leads at the bottom that may then be spread apart,as previously described for direct mating to a motherboard, or may beconnected to a motherboard using a socket 54 or connector specificallydesigned to engage with the bifurcated leads. In the example shown nFIG. 11E, the bifurcated leads include both inner 12 and outer 12′electrode pads which engage with the socket contacts 53.

An elevation view of an electronic subsystem 1 with a clamping collar 38installed is illustrated in FIG. 12A. In this embodiment, a compressionlatch assembly 41 is also shown mounted to the PCB or motherboard 20.Assembly 41 is designed to receive and latch the integrated clampingcollar 38, with attached electrode pads 12 as described for FIG. 11B,into a slot (partially shown with dotted lines) and hold the integratedcollar in compression directly against the PTH annular rings 19, or vias18, or contact pads 21, as previously described. The housing forassembly 41 would typically comprise a rigid, liquid crystal polymer(LCP) plastic or metal and would typically include threaded posts orholes at its ends and mid-point (not shown) for anchoring the housing tothe motherboard using appropriate hardware. Metal spring latches orretention clips 39 located at the ends of the assembly are used to clampthe integrated clamping collar in compression against the motherboardcontacts. These latches or clips 39 would preferably spring outward asthe collar is pressed downward into at least a portion of the slot, andspring back to their original position to latch and hold the collar incompression against the surface of the motherboard once the collar isproperly seated into the slot and sufficient compression is achieved toenable electrical function between all contact surfaces.

The length of the slot and proportionately narrow side rails of thelonger assembly housings 41, may cause the housing and/or motherboardsurface to bow if mated with an integrated collar that contains largenumbers of contacts that require high normal forces to achieve reliableelectrical connection with the motherboard. Consequently, the contactsurfaces near the mid-point of the integrated collar 38 may not receivethe same amount of compressive normal force as the contacts near theends of the collar, causing potential open electrical connections inthis area. To correct this problem, one solution is shown in FIG. 12Ewhere collar 38″ is itself bowed in a convex manner near the mid-pointof its length and in the direction of the motherboard contacts. Whenproperly designed and assembled, the convex-bowed collar 38″ will bringthe electrode pads 12 near the mid-point of its length into directcontact with the motherboard contacts first and enable highercompressive normal forces to be concentrated at this area of themotherboard. The amount of bowing required would be dependant on anumber of factors, including the composition of the collar, whethermetal or plastic, the length and thickness of the collar, the elasticproperties of the complaint material 25, the design of the assemblyhousing and method of anchoring to the motherboard, etc. The skilledartisan can determine the optimal bowing through routine experimentationfor a particular application.

Another solution for solving the tendency of the housing and/ormotherboard surface to bow when mated in compression with the collar isto add an additional metal brace or stiffener plate 45 (FIG. 15A)directly beneath the assembly housing 41 on the opposite side of themotherboard. This metal stiffener plate would provide additionalrigidity to the motherboard, which would be sandwiched in the middlebetween the plate on the bottom and assembly housing on the top surface.The stiffener plate and housing could be assembled together as a unitonto the motherboard using the same hardware (e.g., screws and threadednuts) that clamp both pieces together onto the motherboard. Similar tothe assembly housing described above, the stiffener plate would includean open slot along its length, to avoid metal contact with exposed PTHvias on the bottom of the motherboard, and a means at or near itsmid-point to anchor the side rails of the stiffener plate together withthe side rails of the assembly housing (not shown).

In the embodiment shown in FIG. 12A, the electrode pads includeconductive bumps 17 arrayed across the bottom surface of the integratedclamping collar and are aligned with the PTH vias 18 and PTH annularrings 19 on motherboard 20 by means of alignment posts 58 located nearthe ends of the collar. These posts engage with orientation holes 59(with or without different diameters) placed either on the motherboardor machined or molded into the compression latch assembly housing 41.

FIG. 12B shows a bottom view of the collar 38 of FIG. 12A, with thebifurcated extensions 13 removed for clarity, and FIG. 12C shows abottom view of the same bifurcated extensions of FIG. 12A as they wouldappear with the leads spread apart and bonded to the bottom of thecollar. A narrow open slot 47 is shown extending along the centerlinefor most of the length of collar 38 through which the bifurcations areinserted. Four alignment posts 58 are shown near the ends of the collarand are intended to engage with alignment holes 57 placed at the ends ofthe bifurcations 13. These posts help align the flexible circuit leads16 and conductive bumps 17 with the PTH annular rings 19 and vias 18 onthe PCB motherboard, as described above. It will be understood that thedimensions as shown in FIG. 12C are exemplary only and representative ofthe conventional spacing between conductive bumps 17 to align and engagewith the motherboard PTH vias for a standard 240-pin DIMM socket,although the number of leads and bumps illustrated are reduced forpurposes of clarity. The terminal edge of the bonding adhesive or film9, which is selectively applied to produce bifurcated flexible circuitboard 10, is also shown.

It is well known in the art of designing connector sockets thatgold-plated contacts provide the most reliable electrical interfaces.However, to reduce costs, gold is typically used sparingly byselectively plating the surfaces of the contacts. Large PCB circuits,such as motherboards, are inherently expensive requiring multipleprocess steps during manufacture and risk costly yield losses with eachadditional process step. Therefore, adding even selectively plated golddirectly to the contact pads or vias of a motherboard may beprohibitively expensive. Nevertheless, compression contacts, asdescribed in these embodiments, would perform best when mated withgold-plated surfaces. To adapt the surface of an expensive motherboardfor compatibility with the compression style contacts described herein,a gold-plated interposer board 42 is shown in cross-section in FIG. 12D.This board consists of a thin PCB, flex circuit, or molded-plasticcarrier with an array of plated through hole (PTH) vias 18 to match thefootprint of pads or PTH vias on the motherboard 20 (e.g. FIG. 12A). ThePTH vias 18 on the interposer electrically connect pads or via annularrings 19 from the bottom to the top surface of this carrier. The toppads or annular rings would be selectively gold-plated and would matewith the conductive spheres or bumps 17 of FIG. 12C. The bottom pads orannular rings 19 would be solder coated and/or include solder balls 43suitable for surface mount soldering to the same pattern of pads or PTHvias disposed on the motherboard. In this manner, motherboard contactsthat are typically coated with a non-noble metal such as SnPb areconverted to a gold-plated contact compatible with compression styleconnectors. These carriers can be mass-produced in large panel formatand then cut or stamped to final size or, if manufactured from flexiblecircuits, could be produced in a reel-to-reel or roll-to-roll format andcould be an inexpensive solution for providing an array of gold-platedcontact pads or vias on the motherboard. The interposer 42, as describedherein, may also be used for mating other types of components thatrequire gold-plated contacts for reliable connection to the motherboard(e.g. LCD displays, ribbon-connectors, etc.).

Turning now to FIG. 12E, a different example of a compression styleconnector is illustrated, which retains some features currently found onstandard DIMM type sockets but makes a fundamental change in thelocation of the contacts and direction of the forces applied wheninserting or removing the modules from the socket.

Current DIMM sockets are designed to mate with contact pads arrayedalong the bottom edges on both sides of the memory module's PCBsubstrate. DIMM socket pins apply a lateral normal force against thesepads with approximately 6-8 grams per pin and are designed to rub bothsurfaces of the module's pads as the modules are inserted into thesocket. This ensures that any surface contaminants or oxides present onthe pads are abraded and the pins make good electrical contact with thepads. However, as noted earlier, the number of contact pads hasincreased in recent years to the point that the total amount of forcerequired to insert or extract the modules from these standard sockets iscausing frequent handling damage. The electronic industry currentlyforecasts a need to further increase the number of available contactpads for future memory modules assembled using newer generation DRAMcomponents (e.g. DDR4, DDR5, etc.) to improve the signal-to-noise ratioon controlled-impedance PCB substrates by providing more power andground connections. Many blade server computer OEMs also use veryrestricted enclosures and are straining to reduce the height of thesocket-mounted modules while simultaneously increasing the total memoryavailable on each module. As described below, the design shown in FIG.12E is a major step in resolving these problems.

The electronic subsystem 1 shown in FIG. 12E is similar to FIG. 12A,except that it is integrated with a convex bowed collar 38″, aspreviously described, and includes an alignment post 58 near the centerof its length. This post mates with an orientation hole 59 molded intothe compression latch assembly 41′ and helps to align electrode pads 12,disposed on the bifurcations 13, with a variety of contact pins orsprings, represented in FIGS. 12F-P, that are press-fitted into moldedslots within the base of the plastic-molded frame of assembly 41′.Socket assembly 41′ also includes two latches 51 that are designed torotate about a pivot point and engage with the ends of the convex bowedcollar 38″ to clamp and hold the integrated collar in a state ofcompression against stamped metal socket contacts 60, 61 or 62, that arepress-fitted into the plastic-molded frame or housing of the socket.

Representative examples of the types of pins or spring contacts that canbe incorporated within socket assembly 41′ are illustrated in FIGS.12F-P. FIG. 12F shows pin 60 terminated at its upper tip in a shortrounded point. The same pin is shown in a side-view at 60′ and 60″.These two side-views are identical for this particular pin design, sincethere is no need to produce two versions of the upper contact for 180degrees rotation as illustrated and described below for FIGS. 12J and12M. From the side-view 60′ (and 60″) it can be seen that there is anoffset bend of the stamped-metal socket contact near the mid-point ofits length. This offset bend is shaped such that when pin 60′ is placedin vertical alignment with adjacent pins 60″, which are rotated 180° inorientation as shown in FIGS. 12G-H, the lower portion of the leadsalternate in a staggered pattern when viewed from either the top orbottom (not shown) and are spaced apart by 1.90 mm. FIG. 12G is across-section view taken at location A-A′ of four staggered socket leadspress-fitted into the plastic-molded frame or housing of socket 41′. Thelower portion of the leads is staggered into four rows by rotating pin60″ 180° and placing it immediately adjacent to pin 60′. The upper tipsof adjacent contacts 60′ and 60″ then form two rows that are alignedalong the length of the socket, as shown in FIG. 12H. FIG. 12H is a viewlooking down onto a small section of the molded frame of socket 41′showing that each individual contact tip extends into and is surroundedby a molded slot 40 which provides some freedom of deflection of theupper section on the contacts. As illustrated at 60 in FIG. 12F, eachindividual pin includes a wide “anchoring” section near the mid-point ofits length that is formed during the metal stamping process and whichserves to lock the pin in position when press-fitted into a molded slotat the base of the plastic frame 41′. One embodiment of socket assembly41′ would include a frame with 240 contact pins in four rows that arespaced apart the distances shown in FIG. 12G for compatible assemblyonto motherboards with PTH vias 18 patterned to receive standard 240-pinDIMM sockets.

Turning now to FIG. 12J, contact pin 61 is shown, which appears similarto pin 60 in this view, but when rotated 90 degrees reveals a “J” shapedtermination 61′ that is bent in the (normal) direction of its bottomlead. Pin 61″, though similar to pin 61′, has a reverse “J” bend thatextends in the opposite direction, away from its bottom lead. FIG. 12Kis similar to FIG. 12G and is a cross-section view taken at locationA-A′ of four staggered “J” bend leads press-fitted into theplastic-molded frame or housing of socket 41′. The lower portion of theleads is staggered into four rows by rotating pin 61″ 180° and placingit immediately adjacent to pin 61′. The upper rounded tips of adjacentcontacts 61′ and 61″ then form two upper rows that are aligned along thelength of the socket, as shown in FIG. 12L. FIG. 12L is a view lookingdown onto a small section of the molded frame of socket 41′ showing thateach individual contact tip extends into and is surrounded by a moldedslot 40 which provides some freedom of deflection of the upper sectionon the contacts. Pins 61′ and 61″ are formed differently during themetal stamping process to enable the “J” bends to face in the samedirection (i.e. towards the centerline of frame 41′) along both upperrows, as shown in FIG. 12K. Depending on the cross-sectional dimensions,leaning angle for the upper-section, and type of metal from which thepins are stamped, the “J” bend contact pins 61′ and 61″ can beengineered to deflect when mating with electrode pads 12 to provide awiping action against the pads as described earlier.

Turning now to FIG. 12M, spring contact pin 62 is shown, which whenrotated 90° reveals a “folded” termination 62′ that is bent in the(normal) direction of its bottom lead. Pin 62″, though similar to pin62′, has a reverse bend that extends in the opposite direction, awayfrom its bottom lead. FIG. 12N is similar to FIG. 12K and is across-section view taken at location A-A′ of four staggered “folded”leads press-fitted into the plastic-molded frame or housing of socket41′. The lower portion of the leads is staggered into four rows byrotating pin 62″ 180° and placing it immediately adjacent to pin 62′.The upper rounded tips of adjacent contacts 62′ and 62″ then form twoupper rows that are aligned along the length of the socket, as shown inFIG. 12P. FIG. 12P is a view looking down onto a small section of themolded frame of socket 41′ showing that each individual contact tipextends into and is surrounded by a molded slot 40 which provides somefreedom of deflection of the upper section on the contacts. Pins 62′ and62″ are likewise formed differently during the metal stamping process toenable the folded bends to face in the same direction (i.e. towards thecenterline of frame 41′) along both upper rows, as shown in FIG. 12N.Depending on the cross-sectional dimensions, folded angles for theupper-section, and type of metal from which the pins are stamped, thefolded contact pins 62′ and 62″ can be engineered to deflect when matingwith electrode pads 12 to provide a wiping action against the pads asdescribed earlier.

A preferred embodiment for each of the stamped-metal contacts 60, 61 and62 described above would include selective gold plating over the uppercontact surfaces. The compression latch assembly or socket 41′, as shownin FIG. 12E, includes long leads intended to be inserted through PTHvias 18 formed on the motherboard and soldered to the bottom annularrings 19 of these vias. However, the leads may also be formed withright-angle bends to enable SMT soldering to staggered pads on the topsurface of the motherboard. Assembly 41′, as shown in FIG. 12E, alsoincludes two anchor posts or threaded screws 65 to aid in securing thesocket to the surface of the motherboard during soldering and whenclamping the integrated collar 38″ into place. One preferred method forinserting subassembly 1 into socket 41′ would be (a) engage a first endof the integrated collar 38″ with a first latch 51 of the socket 41′,and (b) apply a downward, cantilever-force on the opposite second end ofcollar 38″ sufficient to engage the second latch of socket 41′ to clampand hold the integrated collar in compression against the socketcontacts.

A cross-section of yet another example of the present invention is shownin FIG. 13. Whereas FIGS. 11 and 12 illustrate a bottom clamping collar38, 38′ or 38″ that does not enclose electronic subsystem 1 or 2, thisexample integrates two metal heat spreaders with angled-flanges 34 thatfully enclose electronic components 11 and passive chips 37 to provide aprotected electronic subsystem 3. The advantages for this designinclude; (a) a rigid enclosure for protecting fragile bare (unpackaged)silicon devices mounted onto flexible substrate 10, (b) an adjacent heatspreading surface for the efficient removal of heat generated by thecontained components 11, (c) electrostatic and electromagnetic shieldingof the contained components 11, (d) a means for enabling a compressiveforce to be applied to contacts arrayed on the bottom surface, and (e) ameans for supporting the module in direct electrical communication withcontacts disposed on the motherboard.

The angled-flange metal heat spreaders 34 comprise two thin,stamped-metal housings that are near mirror images of one another. Thebottom surfaces of both heat spreaders are adhesively bondedrespectively to one of the two bifurcations 13 and are spaced apart fromone another by the thickness of flexible circuit 10. Both legs areseparated and spread apart from one another to form an angle ofapproximately 180°, but they remain joined together where the bondingadhesive or film 9 terminates, as previously shown in FIGS. 1, 6, and11A-B, which in this case is near the gap between the bottom flanges ofthe two heat spreaders shown in FIG. 13. The resulting structure allowsthe two metal heat spreaders to open and close in a clamshell fashionaround the bifurcated flex circuit assembly by a means of a hingeconsisting of flexible extensions 13 and bonding adhesive or film 9.

The angled flanges 34 formed at the bottom of the paired heat spreadersangle outward from the narrower sidewalls and then close back togetherat the base to (a) provide a surface against which a downwardcompression force can be applied by a mating clamping device, (b)provide a flat or slightly angled mounting surface for the flexiblebifurcated extensions, with sufficient width to enable contact with astandard pattern of staggered PTH vias 18 or pads 19 on the motherboardintended for mounting DIMM sockets, (c) provide a means for transferringa compression force to an array of conductive bumps 17 or electrode pads12 (not shown) located on the exposed surface of the bifurcatedextensions 13, (d) form a rigid, expanded cavity for mounting componentsonto the flexible substrate 10 which require greater stand-off height,and/or (e) enable the components 11 and/or passive chips 37 on flexiblecircuit. 10 to be mounted in very close proximity to the surface of themotherboard.

Examples of devices that mate with electronic subsystem 3, for applyinga downward compressive force, are disclosed below in FIGS. 15A-B and16A-C. In these examples, angled wedges contact the outwardangled-flanges 34 of the heat spreaders and apply a clamping forceagainst the flanges, which in turn compress conductive bumps 17 directlyagainst the contact pads, vias or pins on the motherboard. The bottomsurfaces of the flanges may be flat or angled slightly downward, nearthe beginning of the bifurcated extensions, to help compensate for lowercompressive forces resulting from any flexing of the inner edges of theflanges near the bifurcated extensions 13. The downward angled surfacesof the thin metal heat spreaders 34 also provide a means forestablishing compliancy between the conductive spheres or bumps 17,arrayed on the bottom of the folded bifurcated leads, and the contactpads 21 or annular rings 19 surrounding the Plated Thru Via Holes 18 ofthe motherboard. In addition, the adhesive chosen to bond the flexibleleads to the bottom flanges of the heat spreaders can be selected toprovide a measure of compliancy.

The paired metal heat spreaders 34 of electronic subsystem 3 are heldtogether in a closed position surrounding the bifurcated flex circuitassembly by two means; (a) an adhesive-backed Thermal Interface Material(TIM) 36, and (b) interlocking clasps 67 located along the top edge ofthe heat spreaders (ref. FIG. 13). The adhesive-backed TIM 36 is appliedto the interior surface of the metal heat spreaders 34 in a thicknesssufficient to contact and adhere to the backside surfaces of heatgenerating components 11 when the metal heat spreaders are foldedtogether. A suitable TIM would be 3M™ Thermally Conductive Tape 8805,which is supplied with a contact adhesive on both sides of the tape forbonding components together. After cutting two pieces of tape to propersize, a first release liner is removed, exposing a first adhesivesurface, and the tape is applied and pressed against the inside surfaceof both heat spreaders. When the subassembly is ready to be sealed, thesecond release liner is removed from both pieces of tape adhering to theinside surfaces of the heat spreaders, exposing the second adhesivesurface, and the metal heat spreaders are folded and pressed together toadhere the second adhesive surfaces to the backside of the heatgenerating components 11. When folded and pressed together, thethermally conductive interface material 36 bridges and joins the insidesurfaces of the metal heat spreaders and backside surfaces of the heatgenerating components on both sides of the bifurcated flexible circuit10 to form a unified assembly that can be opened, if necessary, forrework, but which otherwise adheres together tenaciously. Additionalmeans for securing the subassembly together is provided by a series ofinterlocking clasps 67 spaced along the top edges of the heat spreaders.As shown in FIG. 13, the upper edges of the heat spreaders overlap oneanother and are formed with interlocking indentations that snap closedwhen the heat spreaders are folded together. Other embodiments ofinterlocking clasps (not shown) would include punched-metal,interdigitated “fingers” that alternate in height above and below anominal midpoint along the top edge of the heat spreaders and whichoverlap and lock together when closed.

In another preferred embodiment of FIG. 13, components 11 comprisememory devices positioned on both sides of the bifurcated flexiblecircuit 10, and immediately above the bottom flange of both heatspreaders, to enable the detached module-height and overallsystem-height of subsystem 3, when mated with motherboard 20, to bereduced to a practical minimum.

FIG. 14 is similar to the embodiment shown in FIG. 13, with exceptionthat the flanges at the bottom of the stamped metal heat spreadersextend inward before flaring outward as two diverging-flanges 35. Thediverging-flanges provide access for applying a downward compressiveforce from directly above the conductive bumps 17.

FIG. 15A is a cross-section view of the subassembly 3, similar to FIG.13, which is directly mated under compression to the DIMM socket PTHvias 18 of motherboard 20. Two metal wedges 49 extend along both sidesof the length of subassembly 3 and include compression pads 44 thatcontact the angled-flanges 34 and surface of the motherboard. The metalwedges may be constructed as separate pieces or from a single slottedcollar that fits over the top of the subassembly 3. A downwardcompressive force is exerted against the angled-flanges when multiplescrews 23 are tightened into a metal stiffener plate 45, similar to thatas previously described that extends the length of subassembly 3 fromthe underside of the motherboard. Conductive bumps 17 align with andpartially extend into the PTH vias 18 to make electrical contact withthe inside perimeter of the annular rings 19.

FIG. 15B is a cross-section view of another embodiment of a subassembly3′, clamped in compression against motherboard 20 as previouslydescribed for FIG. 15A, but which includes a folded extension 10′ of thebifurcated flexible circuit 10 with additional rows of components 11mounted inside non-flanged metal heat spreaders 34′. This foldedextension does not require any flanges on the heat spreaders and enablesadditional rows of components to be connected into circuit with themotherboard through the conductive bumps 17 of one pair of bifurcatedextensions 13 held in compression through a single pair of metal wedges49. By folding the flex circuit extension 10′ over to one side, andinserting its end into a plastic or metal retention clip 74, which isattached to a portion of the metal wedge 49, the total height of thevertically mounted subassembly 3′ is held to a minimum.

Yet another embodiment for a low-profile subassembly 4 is shown in FIG.15C. In this embodiment, subassembly 4 is clamped parallel tomotherboard 20 and the bifurcated flex circuit 10 includes a firstright-angle fold 68 towards the bottom edge of a non-flanged heatspreader 34′ and a second right-angle fold 69 of a first-portion of thebifurcated extensions 13 that is positioned between a lower portion ofthe heat spreader and PTH annular rings 19 of the motherboard. The othersecond-portion of the bifurcated extension includes a third right-anglefold 70 in the opposite direction from that of the first-portion. Thissecond-portion of the bifurcated extension is positioned between acompression pad 44 of clamping device 22 and the PTH annular rings 19 ofthe motherboard 20. In this embodiment, the clamping device 22simultaneously applies a downward compressive force through compressionpads 44 along (a) an upper-portion of the non-flanged metal heatspreader 34″, and (b) the second-portion of the bifurcated extension 13.Screws 23 or other hardware devices can be fastened or threaded into abottom metal stiffener plate 45 or tightened against the plate with alock nut 24. Since the second-portion of the bifurcated extension ispositioned at a different height above the surface of the motherboard, athicker layer of compression pad 44 or different compliant material 25may be needed in areas of clamping device 22 that make direct contactwith the motherboard.

FIG. 15D is similar to FIG. 15B, and illustrates how the low-profilesubassembly 4 of FIG. 15 C can include a folded low-profile subassembly4′ positioned above it. In this embodiment, folded low-profilesubassembly 4′ is electrically connected to the bottom low-profilesubassembly 4 by means of a folded extension 10′ of the bifurcatedflexible circuit 10. Subassembly 4′ is sufficiently spaced abovesubassembly 4 to enable adequate air flow between the adjacentsubassemblies for efficient component cooling and is held in positionwith a plastic or metal retention clip 74′, similar to that shown inFIG. 15B, that is attached to clamping device 22.

Turning now to FIG. 15E, two low-profile subassemblies 4 are positionedabove and below the surface of the motherboard 20. The upper subassemblyis clamped to the motherboard similar to FIG. 15C described above, butthe lower subassembly is connected to the motherboard through a signaltranslation interposer board 56. This board reroutes the signalfunctions coming from the bottom-side of the motherboard so that arecorrectly aligned with the electrode pads on the bifurcated extensions13 of this lower subassembly. If the bifurcated flexible circuits 10 ofthe upper and lower subassemblies were exact mirror images of eachother, the signal translation interposer board would not be required.However, using mirror imaged circuits may be a more expensive solutionthan using a simple signal translation interposed board. The signaltranslation interposer board 56 is preferably pre-attached to thebottom-side of the motherboard 20. However, it may also be pre-attachedto the bifurcated flex circuit 10 and held into compression against thePTH annular rings 19 of the motherboard.

The additional stand-off height caused by the presence of the signaltranslation interposer board 56 may enable various electronic components11 to be soldered to the bottom surface of the motherboard 20 that arethicker than otherwise allowed beneath the upper subassembly, as shownin FIG. 15D. The clamping devices 22 may also use common hardwarefasteners 23 for drawing the clamps together to provide the requiredcompression forces against the upper and lower bifurcated extensions 13of subassemblies 4.

A Direct Connect Socket 5, for easy installment and removal of theprotected electronic subassembly 3 (refer to FIG. 13), is illustrated inFIGS. 16 A-C. To avoid the manufacturing difficulties associated withassembling devices to motherboards using multiple clamps, screws andnuts, a simpler connector concept is shown here that uses a pivotingcompression clamp 48 and compression latch assembly 41″ tosimultaneously apply a downward compression force to both angled-flangesof the metal heat spreaders 34. FIG. 16A is a top view, looking downonto the direct connect socket, while FIG. 16B is a side view of thesame socket. The pivoting compression clamp is attached to thecompression latch assembly with a pivot pin 46 that enables the clamp torotate in a 180° arc in the direction of the arrow. The clamp ispreferably made of a metal or rigid molded plastic as previouslydescribed for the clamping collar 38 of FIG. 11A. However, in thisexample the compression clamp 48 includes two angled compression pads 44that are shaped to conform to the surfaces of the angled-flanges on theheat spreaders. The cross-section A-A′, as shown in FIG. 16C, shows theangled compression pads 44 bonded to the metal or plastic pivoting clamp48.

For this embodiment, the compression latch assembly 41″ is fashionedfrom molded LCP plastic and includes an array of straight,stamped-metal, contact pins 60′ and 60″, as previously described forFIGS. 12E-H, that are press-fitted into the base of the latch assembly.In FIG. 16B, these pins are shown inserted through PTH vias placed onthe motherboard 20 and soldered from the bottom side to the motherboardsimilar to a standard DIMM socket. A metal stiffener plate 45 may or maynot be required, depending on the amount of compression force requiredfor proper operation of the socket and the degree of flexing of themotherboard. It should be noted that the metal stiffener would eitherprovide clearance slots or an insulating surface to prevent electricalshorting of the exposed pins exiting from the bottom of the motherboard.In this embodiment, two screws 23 extend up through the metal stiffener45 and screw into a threaded hole or insert within the compressionlatch.

To operate the Direct Connect Socket 5, shown in FIGS. 16A-C,subassembly 3 is first inserted into the base of the compression latchassembly 41″ and seated in alignment with the pins 60′ and 60″ arrayedacross the bottom. The pivoting compression clamp 48 is then rotatedover and down onto the angled-flanges 34′ of the metal heat spreaders.The open slot 47, as shown in FIGS. 16A and 16C, allows the uppersections of the heat spreaders 34 to pass between the two angledcompression pads 44 and through the compression clamp 48 so that acollar, similar to 38′ of FIG. 11C, extends around the bottom peripheryof subassembly 3. A downward compression force is then applied againstthe angled-flanges 34′ by pressing against the free-end of thecompression clamp 48 until the latch 51 can be engaged to hold the clampin place.

In another embodiment, Direct Connect Socket 5′ (not shown) includesother press-fitted pins or contacts, such as “J-bend” contacts 61′ and61″ or spring contacts 62′ and 62″ previously shown and described forFIGS. 12J-P. In yet another embodiment, Direct Connect Socket 5″ (notshown) does not include any integrated, press-fitted, pins or contactswithin the compression latch assembly 41″, but allows the electrode pads12 or conductive spheres or bumps 17 arrayed on the bifurcatedextensions 13 to directly contact the motherboard PTH vias 18 and/orannular rings 19 as previously shown and described (e.g. FIGS. 6-7). Inyet another embodiment, Direct Connect Socket 5′″ (not shown) allows theelectrode pads 12 to directly contact an array of protruding pins 27from separate “bed-of-nails” connector 26 soldered to the bottom of themotherboard as previously described in FIG. 8A-B.

Another Direct Connect Socket 6, intended to mate with electronicsubassembly 3′ (refer to FIG. 14), is illustrated in FIGS. 17 A-C. Thisembodiment includes many features similar to that described and shown inFIGS. 16A-C. However, this socket uses a bifurcated compression clamp 52that is slightly bowed near its center point and which includes anopen-ended slot 47′ that is not closed at the end. The open-ended slot47′ engages with the diverging-flanges 35 of subassembly 3′ by allowingthe flanges to slide into the slot from the open-end after thebifurcated compression clamp 52 is rotated towards the top of itstravel. The open-ended slot 47′, as shown in FIGS. 17A and C, allows thebifurcated clamp 52 to surround both sides of subassembly 3′ whilesliding along the length of the divergent-flanges 35. When fullyengaged, the bifurcated clamp 52 appears similar to the collar 38 shownin FIGS. 11A and 12A-B, and extends almost completely around the bottomperiphery of subassembly 3′.

As the bifurcated compression clamp is lowered towards the compressionlatch assembly 41″, subassembly 3′ is seated within a molded cavity andis brought into alignment with protruding pins 27 of a “bed-of-nails”connector 26 arrayed across the bottom. The pivoting compression clamp52 is then rotated down against the diverging-flanges 35 of both metalheat spreaders, applying a downward compression force as latch 51 isengaged to retain the clamp in compression. As noted earlier, the bottomof the bifurcated clamp may or may not include a layer of compliantmaterial 25.

In the illustration shown in FIG. 17B, the “bed-of-nails” connector 26is preassembled onto the top surface of the motherboard 20 with thetails of the protruding pins 27 extending down through the PTH vias 18and soldered from the bottom of the motherboard. As noted earlier forFIG. 8A, the “bed-of-nails” connector may also be preassembled on thebottom surface of the motherboard with the protruding pins 27 extendingup through the PTH vias. Various pins may also be press-fitted into thebase of the latch assembly 41″ as previously described for FIG. 16. Thebifurcated compression clamp 52, viewed in this figure, is also slightlybowed near its center point in order to function as previously describedfor the bowed collar 38″ in FIG. 12E.

Turning now to FIGS. 18A-B, a small section of interposer board 42 isshown in cross-section together with a new clamping collar 71 thatincludes a concave-dimpled surface. As previously described for FIG.12D, interposer board 42 is fashioned from a thin PCB, flexible circuit,or molded-plastic carrier. However, instead of containing an array ofplated through hole (PTH) vias 18, this embodiment includes bladedcontacts 63, fashioned from stamped metal with selectively gold-platedtips 72, which are pressed fitted into a thin PCB or plastic moldedinterposer to match the footprint of pads or PTH vias on the motherboard20. The bladed contacts are pointed on the bottom-side of the interposerto aid in their alignment with the PTH vias of the motherboard and inpenetrating the edges of the PTH annular rings 19 when collar 71 appliesa downward compression force from above. The gold-plated tips 72 ofcontacts 63 are aligned with the concave dimples on the bottom surfaceof collar 71 and are rounded at their tips with a radius smaller thanthe radius of the concave dimples. When the thin electrode pads 12,arrayed on the flexible bifurcated extensions 13, are aligned andcompressed between the tips of contacts 63 and concave dimples of collar71, the thin pads 12 are partially deformed into the concave dimples andcreate a “ball and socket” like connection, as shown in the close-upcross-section of FIG. 18B. Electrode pads 12 are typically fashionedfrom thin copper films (≦40 μm thick and finished with a thinnickel-gold coating to resist tarnishing) bonded to thin polyimide films(≦50 μm thick) which can be easily deformed. This type of compressionconnection is intended to improve electrical reliability of theinterposer contacts when (a) they are subject to temperature cyclingduring operation, or (b) the PTH annular rings 19 of motherboard 20 aresolder-coated.

Alternative materials that can be substituted for interposer board 42include polyimide, Mylar, PVC, and PEC films, etc. Alternativecompression-type contacts 63 that can be integrated with interposer 42include gold-fuzz buttons (bumps), isotropic conductive epoxy bumps,copper-plated bumps, etc. (not shown), that are disposed directly aboveand below one another on both sides of the film, similar to that shownin FIG. 18, and are interconnected through small plated or non-platedvias within the film, as shown in FIG. 12D.

FIGS. 18A-B indicate that the concave dimples are arrayed on the bottomsurface of clamping collar 71, which is similar to 38 shown in FIGS. 11Aand B. However, it should be noted, the concave dimples can also beintegrated into the compliant material 25 bonded to the bottom surfaceof collar 38, or fashioned into the bottom surfaces of metal heatspreaders formed with either angled-flanges 34 or divergent-flanges 35(FIGS. 13 and 14).

Turning now to FIGS. 18C-D, a small section of a convex-dimpled clampingcollar 73 is shown in cross-section together with thin electrode pads12, arrayed on a flexible bifurcated extension 13 and aligned above PTHvias 18 and annular rings 19 of motherboard 20. As previously shown anddescribed for FIGS. 9 and 10B and shown again in the close-upcross-section of FIG. 18D, convex dimples will deform the thinbifurcated extension film 13 and bottom electrode pad 12 when a downwardcompressive force is applied through the clamping collar 73, forcing theelectrode pad into electrical contact with the annular ring 19 of themotherboard 20. However, it is preferred with this embodiment andpreviously discussed, that the annular rings on the motherboard includea gold plated finish for this compression contact to form a reliableconnection. In addition, it is desirable that convex dimple radius besmaller than the radius of the PTH via 18 in order for the electrode padto be partially pressed into the via hole, as shown in FIG. 18D. Itshould also be noted, these convex dimples can also be integrated intothe compliant material 25 bonded to the bottom surface of collar 38, orfashioned into the bottom surfaces of metal heat spreaders formed witheither angled-flanges 34 or divergent-flanges 35 (FIGS. 13-14).

As previously described for FIG. 2, the electronic subsystem 1 can beelectrically and mechanically connected to contacts 21 on themotherboard 20 by various means to electrode pads 12 on the flexiblebifurcated extensions 13. In FIG. 15E, it was also demonstrated that twosubassemblies 4′ could be mounted on both top and bottom surfaces of amotherboard 20 and share the same PTH via contacts 19 by means of asignal translation interposer board 56. Turning now to FIG. 19, asimilar embodiment is shown wherein two subsystems 1 are electricallyand mechanically connected to contacts 21 from both sides of motherboard20 by means of another contact translation circuit 66.

Another novel configuration for mounting the electronic subsystem 1 isillustrated in FIG. 20. In this example the bifurcated flexible leadsare opened sufficient to straddle the edge of a PCB or motherboard 20which includes contacts 21 arrayed along its edge. The inner electrodepads 12 of the flexible leads are aligned to these contacts andcompressed together to mechanically and electrically connect theelectronic subsystem in the plane of the motherboard. In the exampleshown, a sliding compression clamp or connector 75 can be moved fromposition A to A′ to lock the aligned bifurcated leads against themotherboard contacts and apply a pinching force that establisheselectrical connections between the inner electrode pads and PCBcontacts. It will be appreciated that once the two halves of thebifurcated flexible leads are aligned, any clamping device may sufficeto enable electrical/mechanical mating of the module to the motherboard.

INDEX OF REFERENCE NUMERALS USED IN THE DRAWING FIGURES

-   1 Electronic Subsystem (with bifurcated flexible circuit board or    substrate)-   1′ Flexed Electronic Subsystem (˜45° clockwise)-   1″ Flexed Electronic Subsystem (˜90° counter-clockwise)-   2 Electronic Subsystem (with rigid circuit board or substrate)-   3 Protected Electronic Subsystem (with angled-flanges)-   3′ Protected Electronic Subsystem (with divergent-flanges)-   3″ Protected Electronic Subsystem (with angled-flanges and folded    extension)-   4 Low-Profile Protected Electronic Subsystem-   5 Direct Connect Socket—Angled Flanges-   6 Direct Connect Socket—Divergent Flanges-   9 Bonding adhesive or film-   10 Bifurcated flexible circuit-   10′ Folded extension-   11 Various electronic components-   12 Inner electrode pads-   12′ Outer electrode pads-   13 Bifurcated extension or leg-   14 Compliant region-   15 Rigid printed circuit board (PCB) daughter card or substrate-   16 Flexible circuit leads-   17 Conductive spheres or bumps-   18 Plated Through Hole (PTH) via-   19 PTH annular ring-   20 Printed Circuit Board (PCB) or motherboard-   21 PCB or motherboard contacts-   22 Clamping device-   22′ Clamping device (with integrated flex circuit connector)-   22″ Clamping device (with integrated compression posts)-   23 Screw or fastener-   24 Lock nut-   25 Compliant material-   26 “Bed-of-nails” connector-   27 Protruding pins-   28 Solder fillet-   29 Compression post-   30 Housing-   30′ Enclosure (full-height)-   30″ Enclosure (reduced-height)-   31 Formed electrode pad-   32 Pierced electrode pad-   33 Slotted portion of the electrode pad-   34 Angled-flange metal heat spreader-   34′ Non-flanged metal heat spreader-   35 Diverging-flange metal heat spreader-   36 Thermal Interface Material (TIM)-   37 Passive chip components-   38 Clamping collar-   38′ Collar with tapered slot-   38″ Convex bowed collar-   39 Spring latch or retention clip-   40 Molded slot-   40′ Angled slots-   41 Compression latch assembly-   41′ Compression latch assembly (with stamped metal leads)-   41″ Compression latch assembly (with pivoting compression clamp)-   42 Interposer-   43 Solder ball-   44 Compression pad(s)-   45 Metal stiffener plate-   46 Pivot pin-   47 Open slot-   47′ Open-ended slot-   48 Pivoting compression clamp-   49 Metal wedge-   50 Flex circuit connector-   51 Latch-   52 Bifurcated compression clamp-   53 Socket contact-   54 Socket housing-   55 Zebra-strip connector-   56 Signal translation interposer board-   57 Alignment hole-   58 Alignment post-   59 Orientation holes-   60 Stamped metal socket contact—straight-   60′ Stamped metal socket contact—straight side-view with normal bend-   60″ Stamped metal socket contact—straight side-view with reverse    bend-   61 Stamped metal socket contact—J-bend-   61′ Stamped metal socket contact—J-bend side-view with normal bend-   61″ Stamped metal socket contact—J-bend side-view with reverse bend-   62 Stamped metal socket contact—spring-   62′ Stamped metal socket contact—spring side-view with normal bend-   62″ Stamped metal socket contact—spring side-view with reverse bend-   63 Interposer contacts-   64 Bifurcated lead—partially reflexed-   64′ Bifurcated lead—fully reflexed-   65 Anchor post or screw-   66 Contacts translation circuit-   67 Interlocking clasp-   68 First fold-   69 Second fold-   70 Third fold-   71 Concave-dimpled clamping collar-   72 Gold-plated tip-   73 Convex-dimpled clamping collar-   74 Plastic or metal retention clip-   75 Sliding compression clamp-   76 Metal contact pin

We claim:
 1. An electrical circuit comprising: a rigid printed circuitboard; a multilayer flexible circuit board having a plurality ofelectrical components on at least one surface thereof, and furtherhaving a bifurcated area along one edge thereof; electrode padsfunctionally connected to said electrical components and positioned onselected surfaces of said bifurcated area of said flexible circuit boardand aligned respectively with electrical contacts on a mechanicalclamping device, said clamping device securing said bifurcated area tosaid rigid printed circuit board when the two legs of said bifurcatedarea are spread apart by about 180°; and, electrical connections betweensaid contacts on said mechanical clamping device and respective lines onsaid rigid printed circuit board so that said rigid printed circuitboard is functionally connected to said flexible circuit board.
 2. Theelectrical circuit of claim 1 wherein said electronic components areselected from the group consisting of: logic devices; memory devices;buffer circuits; timing circuits; analog, digital and mixed-modecircuits; optoelectronic devices; RF devices; resistors; capacitors;inductors; and antennas.
 3. The electrical circuit of claim 1 whereinsaid bifurcated area is spread apart by about 180° with each of said twolegs of said bifurcation respectively forming a selected angle with theplane of the non-bifurcated portion of said flex circuit so that saidflex circuit may be mounted at a selected angle to said rigid printedcircuit board.
 4. The electrical circuit of claim 1 wherein said rigidprinted circuit board is part of a computing device and said multilayerflex circuit comprises a memory module.
 5. The electrical circuit ofclaim 4 wherein said computing device is selected from the groupconsisting of: desktop computers; mobile computers; tablet computers;smart phones; and servers.
 6. The electrical circuit of claim 1 whereineach of said electrode pads further contains a pierced area to enhancemechanical engagement with its respective contact on said motherboard.7. The electrical circuit of claim 6 wherein said pierced area comprisesone or more features selected from the group consisting of: aperturesand slits.